The present invention relates generally to radio antennas, and more particularly to an antenna for portable communication devices.
Wireless handheld communication devices, such as cellular telephones, transmit RF power and are carefully scrutinized for their level of RF radiation emissions. The highest level of RF exposure is most often from RF currents flowing on or in the conductive parts of the housing of the device and not on the antenna. Prior art methods of reducing or eliminating the RF currents of the housing have resulted in the use of large and unwieldy antennas or large RF currents that cause large reactive near fields of the antenna such that it then becomes the dominant source of RF emission. In either case, the size of the antenna and phone increases.
The size of portable communication devices has historically been set by the size of the enclosed electronics and the battery. Consumer and user demand has continued to push a dramatic reduction in the size of communication devices. As a result, during transmission, the antenna induces higher RF current densities onto the small housing, chassis or printed circuit boards of the communication device in an uncontrolled manner. These RF currents are often dissipated rather than efficiently contributing to the radiation of RF communication signals. The dissipation of RF power can detrimentally affect the circuitry on very small units. Moreover, this loss of power lowers the quality of communication and reduces battery life of the device.
Another problem experienced by prior art antennas is the radiation degradation experienced when the portable radio is held and used by the operator. Continuous advances in electronics and battery technology have allowed a dramatic reduction in size, so much so that the performance of the antenna is poor due to it being enclosed by a user""s hand.
The metallic portion of the housing of the portable radio is typically used as the ground or counterpoise for the antenna and allows RF currents to flow in an uncontrolled manner. Unacceptable radiation degradation is typically experienced when an operator places their hand around the housing, thereby causing degradation in the radiation efficiency of the ground radiator.
Accordingly, what is needed is a communication device having a controlled flow of RF currents within the housing of the device so as to remove them from the proximity of the user. It would also be beneficial to provide the capability to adapt current flow to the antenna to improve efficiency. Additionally, it would be an advantage to accomplish these needs without radiation degradation, decreased battery life, or increased size or cost of the communication device.